It is known that foreign objects, such as dirt and portions of string by which the tobacco leaves are tied together during curing, may be separated and removed from tobacco during preliminary processing by the use of a mechanism consisting of a series of elongated roller elements mounted side-by-side in an open frame or bed. Such a mechanism is disclosed in Caudill U.S. Pat. No. 4,809,716.
In such a mechanism the tobacco is transferred across a series of rotating rollers, or "doffer elements", which are covered by cleaning elements such as brushes. Alternatively, the cleaning elements may be a material containing densely packed resilient hook members, such as Velcro.RTM.. The contaminants contained in the tobacco become entwined in the rotating brushes or the Velcro attached to the individual doffer elements. After travelling over the last rotating doffer element, the tobacco is transferred to a separate device, such as a conveyor, and moved to other locations for further processing or storage.
To effectively remove the contaminants from the tobacco, the cleaning brushes or the Velcro must frequently be cleaned of contaminants and periodically replaced. For example, where Velcro.RTM. is employed as the cleaning means, as contaminants become trapped on the cleaning surface, the effectiveness of the cleaning surface is reduced. To "reactivate" the cleaning surface, the trapped contaminants must be removed. Additionally, various portions of the mechanism, such as the doffer elements, require maintenance at unpredictable times. Cleaning, replacement, and maintenance require that the mechanism be inoperable and result in system down time. Maintenance of the mechanism and doffer elements that requires removal of the doffer elements is complicated by the fact that the doffer elements disclosed in the prior art each weighs a great deal.
The maintenance or replacement of doffer elements or other components of the mechanism often require disassembling the entire drive mechanism, resulting in further system down time and labor expenses.
It is known that different varieties and grades of tobacco leaf contain different amounts and different size contaminants, and consist of different tobacco particle sizes. Furthermore, the manner in which the tobacco is packaged, transferred, or stored effects the amount, type and size of foreign objects which may contaminate the tobacco. For instance, tobacco leaves which are transferred in bags made of burlap contain pieces of fibers from the burlap, while tobacco leaves which are tied together with string are contaminated with pieces of string which may be larger than burlap fibers.
It is has also been found that variable spacings between the doffer elements provide optimal cleaning for tobacco known to contain certain types of contaminants. Furthermore, different grades of tobacco, which are of differing densities, require different operating parameters in order to be properly cleaned. For example, testing on Bright tobacco has revealed that a 2-inch horizontal gap between all doffer elements results in optimal separation. Elevation changes between doffer elements are not necessary for Bright tobacco. Testing on Bright has also indicated that up to 50% of entrained contaminants can be removed when the doffer elements are rotated at a speed of 150 rpm and the tobacco feed rate is 8,000 pounds per hour.
Testing on Burley tobacco indicates that optimum operating conditions include horizontal gaps of 3-inches between doffer elements, doffer element rotational speeds of 150 rpm and tobacco feed rate of 8,000 pounds per hour. It has also been concluded that for Oriental tobacco, the optimum set up is a 1.5-inch gap between successive doffer elements, doffer element speed of 150 rpm and tobacco feed rate of 8,000 pounds per hour. It has been found that for both Burley and Oriental tobacco, as well as for Bright tobacco, that the doffer elements should be fixed in the same plane in order the achieve optimal separation.
Although testing on Bright, Burley and Oriental tobaccoes has indicated that change in the elevation of the doffer elements relative to the frame are not prerequisite to successful operation of the mechanism, elevational changes may be useful when other grades of tobacco or other materials must be cleaned of contaminants. The agitation caused by placing one or more doffer elements at a different elevation from the remaining doffer elements may be necessary for cleaning certain materials.
Therefore, it can be seen that the mechanism's operating conditions must be adjustable in order to obtain optimal separation and removal of contaminants from different varieties of tobacco, as well as from other materials.
With respect to mechanisms currently in use, the adjustability of most of the operating conditions is limited. That is, current mechanisms contain an invariable number of doffer elements at fixed horizontal gaps and vertical elevations. Therefore, operating conditions of current mechanisms cannot be varied, or require large amounts of down time to adjust conditions for cleaning different types and grades of tobacco.
Accordingly, it is desirable to provide a doffer mechanism which allows for easy adjustment of both the horizontal gap between successive doffer elements and the vertical elevation of individual doffer elements relative to the frame. It is further desirable for such mechanism to allow for easy removal and replacement of individual doffer elements for maintenance and replacement of the cleaning means.
Further, there is a need for a doffer mechanism which allows for reduced system down time for the cleaning, maintenance, or replacement of the doffer cleaning means and of the doffer mechanism.
Further, there is a need for a doffer mechanism drive design to facilitate such adjustments, cleaning, maintenance, or replacement of doffer cleaning means.
Still further, there is a need for light weight doffer elements to facilitate maintenance, cleaning, and replacement of the doffer mechanism and the doffer elements.
It is an object of the present invention to provide an improved doffer mechanism for removing and separating contaminants and other objects from tobacco.
It is a further object of this invention to provide a doffer mechanism which allows for reduced system down time for cleaning and maintenance of the doffer mechanism and doffer elements.
It is a further object of this invention to provide lightweight doffer elements and a doffer mechanism which allows for easy removal of the doffer elements for maintenance as well as replacement of cleaning elements attached to the doffer elements.
It is also an object of this invention to permit variation in the operating conditions of the mechanism. The mechanism of the present invention allows for easy adjustment of the horizontal gap between successive doffer elements and easy adjustment of the vertical elevation of individual doffer elements relative to the frame to optimize tobacco surface contact with the doffer cleaning means for various types and grades of tobacco. The frames of the mechanism of the present invention can also be installed at an upwardly inclined angle if operating conditions so dictate.
It is a further object of this invention to provide an improved drive design to facilitate such aforementioned adjustments, cleaning, maintenance and replacement of the doffer elements and the cleaning means attached to the doffer elements.